I have seen a critter that is similar to the one in your picture from what I can see. It is a bit far away, and not clear enough for me to see.
. The critter that comes to mind looking at your picture is a Ghost shrimp, the name comes from "National Audubon Society Field Guide to North American Seashore Creatures". I have had these in my 20 gallon tank. They were in some fauna that I retreived from the ocean while fishing. They are more of a brownish-yellow color, to transluscent. The ones I speak of are "pods
" and hangout on the small branches of fauna. As far as I know, they are no harm to yr tank. The ones I had were eaten by the fish in the tank. I have attached a link. I hope this help.